Southern California has become the best-selling market for Mary Jane’s Relaxing Soda, a sugary drink laced with kava, a sedative South Pacific root.

Matt Moody, a nutritional-supplement developer who created the beverage, said the name was an unabashed reference to weed, though the relaxant compounds in kava are chemically unrelated to those in marijuana.

The advertising agency J. Walter Thompson says that Mary Jane’s and other new products such as Slow Cow and Ex Chill are part of a new group of so-called slow-down or anti-energy drinks, which are expected to be one of the top food trends of this year.

The drinks rely on folk medicine sedatives, including kava, chamomile and valerian, to provide an alternative to caffeine-laced and jitter-inducing energy drinks such as Red Bull.

Ann Mack, the director of trendspotting at the agency, said the drinks promote calming and also take on the energy-drink category by claiming to also boost mental focus and concentration.

Travis Arnesen, a spokesman for Ex Drinks in Nevada, said: ”It is a new category, kind of like energy drinks, but designed to relax people. Just recently it has been picking up steam.”

Kava has long been ”a popular recreational drug through much of the Pacific, especially Vanuatu, Fiji, Samoa and Tonga”, said Lamont Lindstrom, a University of Tulsa anthropologist who has studied the plant’s use in Pacific Islander culture.

The calming effect claimed for kava was probably real, said Michael Pollastri, a pharmaceuticals chemist at Boston University.

”If there were not therapeutic effects, it would not be a 1000-year-old folk medicine,” he said.

There are no age limits or restrictions for consumers. Medical experts, however, caution that drinks containing kava and other supplements could have a downside, depending on the chemical compounds used as ingredients and how the plants are processed.

Nathan Scholl, a waiter at a restaurant in Santa Monica, said that he was ”hooked” on the cola-coloured liquid. While the drink did not make him high, he said he found ”the whole Mary Jane thing funny”.

”I drink it after a long day. It takes five or 10 minutes to sink in and then I feel relaxed and slightly euphoric,” he said.